It all started at the Democratic National Convention back in late July when the grieving parents of a Muslim soldier killed in Iraq took the stage to support Hillary Clinton.

U.S. Army Capt. Humayun Khan was killed in Baghdad in 2004.

With his wife standing by his side, Khizr Khan attacked Donald Trump for his (now toned-down) plan to ban all Muslims from the United States.

Hillary Clinton was right when she called my son "the best of America." If it was up to Donald Trump, he never would have been in America. Donald Trump consistently smears the character of Muslims. He disrespects other minorities — women, judges, even his own party leadership. He vows to build walls and ban us from this country.

Donald Trump, you are asking Americans to trust you with our future. Let me ask you: Have you even read the U.S. Constitution? I will gladly lend you my copy. In this document, look for the words "liberty" and "equal protection of law."

Have you ever been to Arlington Cemetery? Go look at the graves of the brave patriots who died defending America — you will see all faiths, genders, and ethnicities.You have sacrificed nothing and no one.

The mother and father of Humayun Khan, a war hero, at the #DemConvention #DemsInPhilly https://t.co/5la2rg83KA

Trump immediately went on the offensive, attacking Khan's wife, Ghazala.

"His wife, if you look at his wife, she was standing there," Trump said in an interview with ABC. "She had nothing to say. She probably, maybe she wasn't allowed to have anything to say. You tell me, but plenty of people have written that. She was extremely quiet and it looked like she had nothing to say."

He also disputed the Khan's claim that Trump had "sacrificed nothing and no one."

"I think I've made a lot of sacrifices. I work very, very hard," he told ABC News.

And then, in true Trump fashion, he took to Twitter to again attack the Khans for supporting Hillary Clinton.

Mr. Khan, who does not know me, viciously attacked me from the stage of the DNC and is now all over T.V. doing the same - Nice!

This story is not about Mr. Khan, who is all over the place doing interviews, but rather RADICAL ISLAMIC TERRORISM and the U.S. Get smart!

The feud went on for days. Shortly after, a Fox News poll found that nearly 70% of respondents said Trump was "out of bounds."

Arizona Sen. John McCain, a former POW during Vietnam, criticized Trump in a statement.

NEW: @SenJohnMcCain on Trump's Khan comments: "It is time for Donald Trump to set the example for our country.